Lithium silicate glass ceramics are characterized by very good mechanical properties, which is why they have been used for a long time in the dental field and there especially for the production of dental crowns and small bridges. The known lithium silicate glass ceramics usually contain, as main components, SiO2, Li2O, Al2O3, alkali metal oxides such as Na2O or K2O and nucleating agents such as P2O5. In addition, they can contain, as further components, for example further alkali metal oxides, alkaline earth metal oxides and ZnO as well as colouring and fluorescent metal oxides in small amounts.
DE 24 51 121 describes lithium disilicate glass ceramics which contain K2O and Al2O3 and P2O5. They are produced from corresponding nuclei-containing starting glasses, which are heated to temperatures of 850 to 870° C. for the crystallization of lithium disilicate.
EP 2 377 830 A1 describes lithium silicate dental glass ceramic which contains 9.0 to 30.0 wt.-% transition metal oxide selected from the group consisting of oxides of yttrium, oxides of transition metals with the atomic number 41 to 79 and mixtures of these oxides. This is characterized by a high refractive index and at the same time very good mechanical and optical properties. The dental glass ceramic contains KAlSiO4 and LaPO4 as further crystal phases. Colorants and/or fluorescent agents, e.g. CeO2, Er2O3 or Tb4O7, can also be present.
WO 2013/053868 A2 relates to lithium silicate glass ceramic which contains hexavalent metal oxide selected from MoO3, WO3 and mixtures thereof in an amount of from 0.1 to 8.4 wt.-% and is suitable for use in dentistry. In addition to lithium silicate, lithium orthophosphate and quartz can be present in the glass ceramic as further crystalline phases.
Known glass ceramics based on lithium silicate can, because of their aesthetically desired optical adaptation to the natural tooth material surrounding them, naturally only be distinguished from the latter with difficulty. This also applies to known fluorescent glass ceramics since the fluorescent agents added to them serve to imitate to a great extent the fluorescence of the natural tooth material.